Multilayer films

Abstract

There is provided a multilayer film comprising a starch layer and at least one other layer. The multilayer film has excellent barrier properties. The starch layer comprises a modified starch having a degree of substitution less than 1.5. Suitable other layers include polyolefins. The multilayer film finds use in packaging, particularly in packaging foodstuffs.

The invention claimed is: 
     
       1. A multilayer film comprising:
 (a) at least one starch layer comprising a modified starch; and 
 (b) at least one other layer having a water vapour permeability coefficient less than 1 g.mm/m 2 .24hr.atm measured at 38° C. and 90% relative humidity; and 
 wherein the total thickness of the at least one starch layer is in the range of from about 50 to about 150 microns and is greater than 20% of the total thickness of the multilayer film, wherein the modified starch has a degree of substitution less than 1.5; 
 wherein the multilayer film has an oxygen permeability coefficient (OPC) that remains below 0.2 cm 3  mm/m 2 .24h.atm at 75% relative humidity for at least 10 days, wherein the OPC is normalised to 1 mm sample thickness and is based on starch layer thickness. 
 
     
     
       2. The multilayer film according to  claim 1 , wherein the multilayer film has an oxygen permeability coefficient (OPC) that remain below 0.1 cm 3  mm/m 2 .24h.atm at 75% relative humidity for at least 10 days. 
     
     
       3. The multilayer film according to  claim 1 , wherein the multilayer film has an oxygen permeability coefficient (OPC) less than 0.6 cm 3  mm/m 2 .24h.atm at 50% RH. 
     
     
       4. The multilayer film according to  claim 1 , wherein the water vapour permeability coefficient of the at least one other layer is less than 0.5 g.mm/m 2 .24hr.atm. 
     
     
       5. The multilayer film according to  claim 1 , wherein the total thickness of the at least one starch layer is at least about 100 microns. 
     
     
       6. The multilayer film according to  claim 1 , wherein the at least one other layer comprises a polyolefin, polyethylene terephthalate, nylon, polyvinylchloride and polyvinylidene dichloride or mixtures thereof. 
     
     
       7. The multilayer film according to  claim 6 , wherein the polyolefin is selected from the group consisting of high density polyethylene, low density polyethylene, linear low density polyethylene, polypropylene, biaxially orientated polypropylene and mixtures thereof. 
     
     
       8. The multilayer film according to  claim 1 , wherein the multilayer film comprises an inner starch layer and two outer layers. 
     
     
       9. The multilayer film according to  claim 1 , wherein the at least one starch layer is fixed to the at least one other layer by an adhesive. 
     
     
       10. The multilayer film according to  claim 1 , wherein the modified starch comprises a high amylose starch. 
     
     
       11. The multilayer film according to  claim 1 , wherein the modified starch is chemically modified to include a hydroxyalkyl C 2-6  group or modified by reaction with an anhydride of a carboxylic acid. 
     
     
       12. The multilayer film according to  claim 1 , wherein the at least one starch layer further comprises at least one water soluble polymer. 
     
     
       13. The multilayer film according to  claim 12 , wherein the at least one water soluble polymer is selected from the group consisting of polyvinyl alcohol and polyvinyl acetate and mixtures thereof. 
     
     
       14. The multilayer film according to  claim 1 , wherein the at least one starch layer further comprises at least one plasticiser. 
     
     
       15. The multilayer film according to  claim 14 , wherein the at least one plasticiser comprises one or more polyols. 
     
     
       16. The multilayer film according to  claim 1 , wherein the at least one starch layer comprises one or more nanomaterials. 
     
     
       17. The multilayer film according to  claim 16 , wherein the nanomaterials comprise clay or modified clay or both. 
     
     
       18. A method of making the multilayer film according to  claim 1 , wherein the method comprises at least one of the steps of co-extrusion, coating, casting or film blowing. 
     
     
       19. Packaging comprising the multilayer film according to  claim 1 .